1. Field of the Invention
The invention relates to an injector for a flotation cell, comprising a feed channel for feeding a fibre suspension flow to the flotation cell, a flow distribution element for distributing the fibre suspension flow fed to the injector into partial flows, a mixing apparatus for mixing air with the fibre suspension, and at least one air input point for sucking air to be mixed with the fibre suspension into the injector.
The invention further relates to a flotation cell for removing ink or impurities from a fibre suspension.
The invention still further relates to a method of feeding a fibre suspension flow to a flotation cell comprising an injector comprising a feed channel for feeding the fibre suspension flow to the flotation cell, a flow distribution element for distributing the fibre suspension flow fed to the injector into partial flows, a mixing apparatus for mixing air with the fibre suspension, and at least one air input point for sucking air to be mixed with the fibre suspension into the injector, the method comprising feeding the fibre suspension flow to the injector, distributing the fibre suspension flow to be fed to the injector into partial flows so that the partial flows suck air to be mixed with the fibre suspension flow into the injector, feeding the partial flows of the fibre suspension flow to a mixing apparatus constituting a pre-mixing phase, whereby the partial flows carry the air sucked into the injector by the partial flows to the pre-mixing phase, and mixing in the pre-mixing phase the air carried by the partial flows to the pre-mixing phase with the partial flows.
2. Description of Related Art
Flotation cells, i.e. flotation containers, are used for removing ink and other impurities from a fibre suspension produced from disintegrated and sorted recycled paper. This process is also called deinking. The purpose of deinking is to obtain as white and clean recycled fibre pulp as possible. Flotation cells are used in flotation deinking, where flotation is performed in cells by adding, as a flotation chemical, soap or another flotation stimulating and surface tension preventing chemical to a diluted, approximately 1-% fibre suspension. In addition, air is mixed with the fibre suspension. Ink and other impurities adhere to air bubbles that rise to the surface of the fibre suspension, enabling the ink and other impurities to be removed from the surface of the fibre suspension by using overflow or scraping.
U.S. Pat. No. 5,465,848 discloses a typical flotation cell which includes an injector provided with a feed channel for introducing a fibre suspension to be purified to the flotation cell. In addition to the feed channel, the injector comprises an aperture plate which serves as a flow distribution element for dividing the fibre suspension flow to be fed to the flotation cell into smaller partial flows. Downstream of the aperture plate and at a distance therefrom, tube sections are provided which form a mixing apparatus and in which partial flows of the fibre suspension flow emerging through the apertures of the aperture plate and air to be fed to the injector are pre-mixed with one another. Air is fed to the injector via an air intake point arranged between the aperture plate and the tube sections on the side of the injector so that the air to be fed to the injector is carried by the partial flows to the mixing apparatus constituting a premixing phase.
A problem with flotation cells and injectors in particular of the kind disclosed in U.S. Pat. No. 5,465,848 is that the injector difficult to clean since it lacks unobstructed access to the aperture plate of the injector and the tube sections constituting the mixing apparatus for their washing and flushing without dismantling the entire injector. In addition, a feed pipe extending high above the roof of the flotation cell and manifold pipes to be placed therefore at least partly high above the roof of the flotation cell for conveying the fibre suspension from the pulp processing devices to the flotation cells take a considerable structural space, which increases the total height of the flotation cell system and thus the need for space in the vertical direction so that in the case of two superimposed flotation cells, for instance, the need for space is doubled.